1. Field of the Invention
The present invention relates to a guide apparatus for biaxial shifting motion and uniaxial turning motion.
2. Description of the Related Art
There has already been known a guide apparatus for biaxial shifting motion and uniaxial turning motion disclosed for example in Japanese Patent Provisional Publication No. H8-99243.
In the above-mentioned guide apparatus, a linear motion guide apparatus composed of a guide rail and a movable block is combined with the other linear motion guide apparatus having the same structure so that the movable block of the former is pivotably connected through a pivot supporting mechanism to the movable block of the latter. The guide rail of the former linear motion guide apparatus is fixed to a base and the guide rail of the latter liner motion guide apparatus is fixed to a table. A plurality of guide apparatus each having such a structure are used to form a table for biaxial shifting motion and uniaxial turning motion.
The above-described conventional guide apparatus for biaxial shifting motion and uniaxial turning motion however has the following problems.
In the conventional guide apparatus, two guide rails defining biaxial directions respectively turn on the plane defined by the biaxial lines. As a result, there is difficulty in control of turning motion at a point other than the origin of the coordinate axes and of shifting motion in longitudinal and lateral directions (i.e., X and Y directions) after the turn by a prescribed turning angle. When a table 103 turns as shown in FIG. 11 at the origin of the coordinate axes with the use of three sets of guide apparatus for biaxial shifting motion and uniaxial turning motion 100, 101, 102, movable guide rails 100Y, 101X, 102X of the guide apparatus 100, 101, 102 incline relative to stationary guide rails 100X, 101Y, 102Y. A translation operation of the table 103 from the above-mentioned condition requires a parallel movement of each of the movable guide rails 100Y, 101X, 102X as well as a proper maintenance of the inclined angle of the movable guide rails 100Y, 101X, 102X relative to the stationary guide rails 100OX, 101Y, 102Y, thus leading to an extremely complex control.
It is actually difficult to dispose the pivot supporting mechanism between the movable blocks of the linear motion guide apparatus. More specifically, when the pivot supporting mechanism having outer and inner rings is disposed between the movable blocks, the outer ring is for example secured to one of the movable blocks and the inner ring is secured to the other of them. Accordingly, it is necessary to form a hole on the one movable block, into which the outer ring can be fitted, to form a projection on the other movable block, which can be fitted into the inner surface of the inner ring, and to provide a means for preventing the pivot supporting mechanism from coming out, thus requiring a complex structure.
There is also required a proper squareness of the bottom surface of each of the guide rails secured to the base and the table, respectively, relative to the pivot axis of each of the pivot supporting mechanisms. The squareness is determined for example by the fitting surfaces of the outer ring and the portion of the one movable block, which forms the hole as well as the fitting surfaces of the inner ring and the projection formed on the other movable block, as described above. Combination of a working error in diametrical length of the hole formed on the one movable block with an improper squareness of the inner peripheral surface of the portion of the one movable block, which forms the hole, combination of a working error in diametrical length of the outer periphery of the projection formed on the other movable block with an improper squareness of the outer peripheral surface of the projection, and combination of working errors in an outer diametrical length of the outer ring and an inner diametrical length of the inner ring are complicated and there cannot be obtained a proper squareness of the bottom surface of the guide rail relative to the pivot axis of the pivot supporting mechanism.
An improper squareness causes a wavy movement of the table when the table turns, thus making it impossible to carry out a positional determination with high precision. A conceivable method of disposing a guide mechanism between the movable blocks in order to obtain a proper squareness leads to a complicated structure.
A plurality of holes for bolts for fixing the guide rails to the table are required to be formed thereon. In this case, it is necessary to apply a precise working to the table to form the hole with a prescribed proper pitch.
When force is applied to the table at a position apart from the pivot axis of the guide apparatus for biaxial shifting motion and uniaxial turning motion, a moment load having a function of inclining the pivot axis is applied to the pivot supporting mechanism. The moment load is applied through the guide rail to the pivot supporting mechanism so that the moment load is amplified by an amount corresponding to the length of the guide rail. Accordingly, a large displacement occurs at the pivot axis and the inclination angle of the table increases, thus leading to a poor positional determination.